Prompt not returning null?

Question

I have a prompt at the beginning of my page, and the text of a header is changed depending on the user's input. Since clicking the Cancel button returns null and clicking the Ok button without any text entered in the field returns an empty string, I used the two checks in my code to alter the text accordingly. The issue is that the prompt isn't actually returning null when the Cancel button is clicked. It is instead returning it as a string.

Javascript:

var name = prompt("Enter your name");
var header = document.getElementById("welcome-header");

if (name !== "null" && name !== "") {
    header.innerHTML = `Welcome, ${name}!`;
}

To accommodate for this, I had to actually put null in a string, as shown in the code snippet. Am I missing something?

Here's where W3 shows that it should return null.

Why is the prompt not returning null? if I change the if statement to: if (name !== null) {...} it stops working. — Chris Lallo, Feb 25 '19 at 02:53
I was even more confused when I came across the error, because I had recently been utilizing prompts when messing around, and it worked just fine when checking for null values. It doesn't do that here, though — Chris Lallo, Feb 25 '19 at 02:55
@ChrisLallo your code does return `null` when you click the cancel button, it just returns an empty string when you click ok with an empty input https://jsfiddle.net/k0fmwvep/ — Nick Parsons, Feb 25 '19 at 02:57
**Duplicate, see this question:** https://stackoverflow.com/questions/38597356/why-prompt-returns-sometimes-null-as-string — Ele, Feb 25 '19 at 02:58

score 0 · Answer 1 · answered Feb 25 '19 at 02:45

0

You can just do a falsy check:

if (!name) {...}

answered Feb 25 '19 at 02:45

Jack Bashford

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Works fine for null values, but not for when I enter actual strings – Chris Lallo Feb 25 '19 at 02:47

lacostenycoder · Answer 2 · 2019-02-25T03:26:02.847

0

Try this, you should not care if it's null, if it's not null it should have a length of > 0 but you can just use simple regex to look for any word in case only blank spaces are entered. Not sure why null is getting passed as a string, I can't duplicate that behavior but if it's an edge case, try:

if (name != 'null' && name.match(/\w/).length > 0 {
    header.innerHTML = `Welcome, ${name}!`;
}

edited Feb 25 '19 at 03:26

answered Feb 25 '19 at 02:56

lacostenycoder

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Still allows for null to pass through (clicking "Cancel" displays 'Welcome, null!') – Chris Lallo Feb 25 '19 at 02:57
what browser are you using? that seems odd – lacostenycoder Feb 25 '19 at 02:58
see updated answer – lacostenycoder Feb 25 '19 at 03:26
See comments on the main thread – Chris Lallo Feb 25 '19 at 03:29
@ChrisLallo ok but you will get same problem if someone enters the space bar 2x or more then hit ok, so you'll still have a bug without the regex example I've given here – lacostenycoder Feb 25 '19 at 03:32

Prompt not returning null?

2 Answers2